► In the modern era of wirelesscommunications, radios are becoming increasingly more cognitive. As the complexity and robustness of friendly communications increases, so do the…
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▼ In the modern era of wirelesscommunications, radios are becoming increasingly more cognitive. As the complexity and robustness of friendly communications increases, so do the abilities of adversarial jammers. The potential uses and threats of these jammers directly pertain to fourth generation (4G) communication standards, as well as future standards employing similar physical layer technologies.
This paper investigates a number of threats to the technologies utilized by 4G and future systems, as well as potential improvements to the security and robustness of these communications systems. The work undertaken highlights potential attacks at both the physical layer and the multiple access control (MAC) layer along with improvements to the technologies which they target.
This work presents a series of intelligent, targeted jamming attacks against the orthogonal frequency division multiplexing (OFDM) synchronization process to demonstrate some security flaws in existing 4G technology, as well as to highlight some of the potential tools of a cognitive electronic warfare attack device. Performance analysis of the OFDM synchronization process are demonstrated in the presence of the efficient attacks, where in many cases complete denial of service is induced.
A method for cross ambiguity function (CAF) based OFDM synchronization is presented as a security and mitigation tactic for 4G devices in the context of cognitive warfare scenarios. The method is shown to maintain comparable performance to other correlation based synchronization estimators while offering the benefit of a disguised preamble. Sync-amble randomization is also discussed as a combinatory strategy with CAF based OFDM synchronization to prevent cognitive jammers for tracking and targeting OFDM synchronization.
Finally, this work presents a method for dynamic spectrum access (DSA) enabled radio identification based solely on radio frequency (RF) observation. This method represents the framework for which both the cognitive jammer and anti-jam radio would perform cognitive sensing in order to utilize the intelligent physical layer attack and mitigation strategies previously discussed. The identification algorithm is shown to be theoretically effective in classifying and identifying two DSA radios with distinct operating policies.
Advisors/Committee Members: Clancy, Thomas Charles (committeechair), McGwier, Robert W. (committeechair), Reed, Jeffrey H. (committee member), Hancock, Kathleen (committee member), Shukla, Sandeep K. (committee member).

▼ As the data rates and performance of current telecommunications technologies reach their limits, MIMO offers promising results allowing for higher spectral efficiencies (or capacities) through the use of multiple element antennas (MEAs). Conventional testing methods, however, cannot be used for multi-antenna systems due to the co-dependence of antenna and RF effects, and baseband hardware and software design. This dissertation specifies a novel MIMO-OFDM, BLAST-based testing design using a hybrid FPGA/DSP development platform from Lyrtech. The design allows for rapid implementation and a consistent indication of the channel impulse response. In addition, a multipath environment is further created to mimic a realistic high scattering scenario. A study of MIMO system capacity is performed along with measurements of an actual over-the-air (OTA) channel. Observations about capacity and the effect of MEA antenna separations are then drawn and conclusions made as to the overall ability to effectively test MIMO systems. The platform used is the result of efforts from several individuals within UW's CST group. My contributions and research are documented in this dissertation.

▼ Accurate channel knowledge is indispensable to the practical success of channel-aware wireless communication technologies. However, channel estimates obtained from pilot symbols rapidly become outdated due to fast time variations of multipath fading channels.
To reduce system cost, antenna subset selection reduces radio frequency (RF) chain components. For systems selecting a subset of a plurality of antennas for reception, this outdated channel information is a significant impediment to selection and data decoding reliability.
In this thesis, training-based schemes for antenna selection (AS) for time-varying channels which account for practical constraints such as training, packetization and antenna switching time are proposed based on discrete prolate spheroidal sequences. They only operate with knowledge or estimates of the Doppler frequency and the channel signal-to-noise ratio (SNR), but do not require detailed statistical correlation knowledge.
A pilot-based AS scheme for time-varying frequency-flat channels for single input-multiple output (SIMO) systems selecting one of a plurality of antennas using packet or symbol-rate antenna switching is first proposed. It is demonstrated that the presented scheme provides significant performance gain over AS methods using Fourier-based orthogonal training as well as over single antenna systems with perfect channel knowledge. Analytical expressions for the symbol error probability (SEP) of M-ary phase-shift keying (MPSK) for systems employing the suggested techniques are provided.
The second part of this thesis investigates the more general case of selecting a subset of a plurality of receive antennas. A new pilot-based receive antenna subset selection algorithm for time-varying frequency-flat channels is presented. The proposed AS algorithm is shown to outperform AS methods based on Fourier prediction/estimation as well as SIMO systems with perfect channel knowledge. Analysis of MPSK and quadrature amplitude modulation (MQAM) SEP for systems with receive AS is provided.
The combination of AS and orthogonal frequency division multiplexing (OFDM) over the more realistic time-varying and frequency-selective fading scenario is examined in the final part. Training schemes for receive AS using packet-rate antenna switching for SIMO and multiple input-multiple output (MIMO) OFDM systems are developed. The suggested schemes exhibit a superior performance over AS methods using either linear interpolation/extrapolation or Fourier prediction/estimation techniques.

► It is well known that multipath effects cause inter-symbol interference (ISI) for high-speed signaling and ultimately limit the achievable data rate at any frequency band.…
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▼ It is well known that multipath effects cause inter-symbol interference (ISI) for high-speed signaling and ultimately limit the achievable data rate at any frequency band. In this thesis, we study several different methods to tackle this issue and provide solutions for establishing efficient wireless links that can provide several Gbps data rate. Specifically, we show that proper choice of polarization, when used with the proposed topology detection algorithm reduces the multipath in 60 GHz wireless channel and increases the error-performance of the network. We also develop a direction-detection algorithm for directional communications in 60 GHz, which is proven to be effective in reducing multipath and increasing spatial diversity. Finally, we propose a double directional channel model for 60 GHz channel as a modification to IEEE 802.15.3c channel model to include the effects of directional antennas both on the transmitter and the receiver side.
Advisors/Committee Members: Liu, Huaping (advisor), Magana, Mario (committee member).

► The rapid growth of mobile telephone use, satellite services, and now the wireless Internet and WLANs are generating tremendous changes in telecommunication and networking. As…
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▼ The rapid growth of mobile telephone use, satellite services, and now the wireless Internet and WLANs are generating tremendous changes in telecommunication and networking. As indoor wirelesscommunications become more prevalent, modeling indoor radio wave propagation in populated environments is a topic of significant interest. Wireless MIMO communication exploits phenomena such as multipath propagation to increase data throughput and range, or reduce bit error rates, rather than attempting to eliminate effects of multipath propagation as traditional SISO communication systems seek to do. The MIMO approach can yield significant gains for both link and network capacities, with no additional transmitting power or bandwidth consumption when compared to conventional single-array diversity methods. When MIMO and OFDM systems are combined and deployed in a suitable rich scattering environment such as indoors, a significant capacity gain can be observed due to the assurance of multipath propagation. Channel variations can occur as a result of movement of personnel, industrial machinery, vehicles and other equipment moving within the indoor environment. The time-varying effects on the propagation channel in populated indoor environments depend on the different pedestrian traffic conditions and the particular type of environment considered. A systematic measurement campaign to study pedestrian movement effects in indoor MIMO-OFDM channels has not yet been fully undertaken. Measuring channel variations caused by the relative positioning of pedestrians is essential in the study of indoor MIMO-OFDM broadband wireless networks. Theoretically, due to high multipath scattering, an increase in MIMO-OFDM channel capacity is expected when pedestrians are present. However, measurements indicate that some reductions in channel capacity could be observed as the number of pedestrians approaches 10 due to a reduction in multipath conditions as more human bodies absorb the wireless signals. This dissertation presents a systematic characterization of the effects of pedestrians in indoor MIMO-OFDM channels. Measurement results, using the MIMO-OFDM channel sounder developed at the CSIRO ICT Centre, have been validated by a customized Geometric Optics-based ray tracing simulation. Based on measured and simulated MIMO-OFDM channel capacity and MIMO-OFDM capacity dynamic range, an improved deterministic model for MIMO-OFDM channels in indoor populated environments is presented. The model can be used for the design and analysis of future WLAN to be deployed in indoor environments. The results obtained show that, in both Fixed SNR and Fixed Tx for deterministic condition, the channel capacity dynamic range rose with the number of pedestrians as well as with the number of antenna combinations. In random scenarios with 10 pedestrians, an increment in channel capacity of up to 0.89 bits/sec/Hz in Fixed SNR and up to 1.52 bits/sec/Hz in Fixed Tx has been recorded compared to the one pedestrian scenario. In addition, from the results a maximum increase…

► Due to the proliferation of data-hungry applications in smartphones and other personal mobile devices, the demand for higher data rate is increasing. This phenomenon has…
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▼ Due to the proliferation of data-hungry applications in smartphones and other personal mobile devices, the demand for higher data rate is increasing. This phenomenon has a huge impact on architecture of wireless cellular networks. Based on this fact, the architecture of wireless cellular networks is transforming from voice-centric and centrally-controlled to the data-centric and distributed, in order to address the massive data demand of users.One efficient approach to implement the data-centric and distributed wireless cellular networks is wireless heterogeneous cellular networks (HCN), where a multitude of radio access points with different technologies and platforms can interoperate flexibly and intelligently. However, augmenting the conventional wireless cellular networks with access points of different characteristics will introduce new challenges in integrating different access points to reach seamless connectivity.In order to address the broad range of challenges we face in HCNs, the need for efficient and accurate model to capture the main features of wireless networks is paramount. The proposed model should be general but not too complicated to be difficult to gain insight. Stochastic geometry has been proven to be a powerful mathematical tool in modeling wireless networks with irregular topologies. In this work, we incorporate principles from stochastic geometry by modeling the wireless networks via using point processes such as Poisson point process (PPP) and Binomial point process (BPP).To be more specific, we have exploited the PPP model in modeling wireless HCNs, while BPP model is used to model wireless ad hoc networks.In this thesis, we first analyze the performance of finite wireless networks in the context of wireless ad hoc networks and wireless HCNs. The significance of this part is emphasized by this fact that, in most practical scenarios the number of wireless nodes and access points is predefined and fixed and they are deployed in a finite region. The network performance is measured from different aspects such as interference distribution, outage probability, throughput, capacity, and cell association area. In all of these scenarios, we incorporate signal-to-interference-plus-noise ratio (SINR) metrics to measure the performance of different multiple access channel schemes and association protocols.In the second part of this thesis, we focus on wireless HCNs using the PPP model where the number of nodes and size of the deployed region can be arbitrarily large. Most of previous works focus on the case that only downlink or uplink (not both) transmissions are possible at a given channel spectrum and instant of time. In this work, we derive the network performance for decoupled association and concurrent uplink and downlink transmissions. Furthermore, different traffic patterns are studied to highlight its contribution on network performance.Finally, in the last part of the thesis, we consider the cellular-based machine type communication, where a massive number of machine type devices are…
Advisors/Committee Members: Reed, Mark, Engineering & Information Technology, UNSW Canberra, UNSW, Aboutorab, Neda, Engineering & Information Technology, UNSW Canberra, UNSW, Pickering , Mark, Engineering & Information Technology, UNSW Canberra, UNSW.

► The main purpose in wirelesscommunications is to allow high data rates, low delays, high net capacity and flexibility in services. The Direct Spreading –…
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▼ The main purpose in wirelesscommunications is to allow high data rates, low delays, high net capacity and flexibility in services. The Direct Spreading – Code Division Multiple Access (DS-CDMA) technology is the main key to combat several sources of interference.
The Intersymbol Interference (ISI) tends to increase with the increase in the symbol rates. To combat the ISI, this thesis improve the ISI Cancellation System, named “Commutation Signaling”. Additionally, presents the use of DS-CDMA technology, and because all the spectrum is available to all users at the same time, there is Multiple Access Interference (MAI), which is caused because several spreading codes used by several users are not received by one reference user perfectly orthogonal.
This thesis studies Subtractive Multi-User Detectors (SIC – Successive Interference Cancellation, and PIC – Parallel Interference Cancellation) without and with the ISI Cancellation System – Commutation Signaling. Additionally, studies the detection with Noise Whitening Matched Filter (NWMF) that combats the MAI with the whitening of the interference power spectrum, and so, following the Single-User strategy, also without and with the ISI Cancellation System – Commutation Signaling.

► The main purpose in wirelesscommunications is to allow high data rates, low delays, high net capacity and flexibility in services. The Direct Spreading –…
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▼ The main purpose in wirelesscommunications is to allow high data rates, low delays, high net capacity and flexibility in services. The Direct Spreading – Code Division Multiple Access (DS-CDMA) technology is the main key to combat several sources of interference.
The Intersymbol Interference (ISI) tends to increase with the increase in the symbol rates. To combat the ISI, this thesis improve the ISI Cancellation System, named “Commutation Signaling”. Additionally, presents the use of DS-CDMA technology, and because all the spectrum is available to all users at the same time, there is Multiple Access Interference (MAI), which is caused because several spreading codes used by several users are not received by one reference user perfectly orthogonal.
This thesis studies Subtractive Multi-User Detectors (SIC – Successive Interference Cancellation, and PIC – Parallel Interference Cancellation) without and with the ISI Cancellation System – Commutation Signaling. Additionally, studies the detection with Noise Whitening Matched Filter (NWMF) that combats the MAI with the whitening of the interference power spectrum, and so, following the Single-User strategy, also without and with the ISI Cancellation System – Commutation Signaling.

► Recently, massive MIMO (multiple-input-multiple-output) systems, where the base station (BS) is equipped with hundreds of small, low-cost, and low-power antennas, have been proposed as one…
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▼ Recently, massive MIMO
(multiple-input-multiple-output) systems, where the base station
(BS) is equipped with hundreds of small, low-cost, and low-power
antennas, have been proposed as one of the promising technologies
for the next generation cellular systems. The thesis works on the
performance analysis of single-cell multi-user massive MIMO
downlink. Perfect channel state information (CSI) is assumed at the
BS and maximum ratio transmission (MRT) precoding scheme is
adopted. We first investigate the distribution of the interference
power and derive its probability density function (pdf) by central
limit theory. After that, analytical results on the outage
probability and the sum-rate are derived. Different to existing
work using the law of large numbers to derive the asymptotic
deterministic signal-to-interference-plus-noise-ratio (SINR), the
randomness of the interference in the SINR is kept intact in our
work, which allows the derivation of the outage probability. We
further extend to networks with per-antenna power constraint. A
modified MRT precoding scheme is proposed and the performance of
the modified scheme is analyzed. Our work show that the modified
MRT precoding can achieve lower outage probability and higher
sum-rate than MRT precoding, even with more strict power
constraint.

► In recent years, the wireless data traffic grew exponentially, which was further accompanied by an increasing demand for higher data rates. Towards this aim, Terahertz…
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▼ In recent years, the wireless data traffic grew exponentially, which was further accompanied by an increasing demand for higher data rates. Towards this aim, Terahertz band (0.1-10 THz) communication is envisioned as one of the key wireless technologies of the next decade. The THz band will help to overcome the spectrum scarcity problems and capacity limitations of current wireless networks, by providing an unprecedentedly large bandwidth. In addition, THz band communication will enable a plethora of long-awaited applications ranging from instantaneous massive data transfer among nearby devices in ultra-high-speed wireless personal and local area networks, to ultra-high-definition content streaming over mobile devices in 5G and beyond small cells. The objective of the thesis is to establish the physical layer foundations of the ultra- broadband communication in the THz band. First, a unified multi-path propagation channel is modeled in the THz band, based on ray-tracing techniques. The wideband characterization are analyzed, which include the distance-varying spectral windows, the delay spread, the wideband capacity and the temporal broadening effects. Second, a multi-wideband waveform design for the THz band is proposed to improve the distance and support ultra- high-speed transmissions. Third, two algorithms for timing acquisition in the pulse-based wireless systems are developed, namely the low-sampling-rate (LSR) algorithm, and the maximum likelihood (ML)-based approach. Fourth, the distance-aware bandwidth resource allocation schemes for the single-user and multi-user THz band networks are developed. Fifth, a three-dimensional (3-D) end-to-end model is developed and characterized, which includes the responses of the graphene-based reflectarray antenna and the 3-D multi-path propagation. The provided physical layer analysis in this thesis lays out the foundation for reliable and efficient ultra-high-speed wirelesscommunications in the THz band.
Advisors/Committee Members: Akyildiz, Ian F. (committee member), Li, Geoffrey Ye (committee member), Weitnauer, Mary Ann (committee member), Sivakumar, Raghupathy (committee member), Jornet, Josep Miquel (committee member).

► In order to introduce the benefits of Multiple-Input/Multiple-Output (MIMO) wireless solutions into the airborne environment for maximal effect, the airborne channel must be fully understood.…
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▼ In order to introduce the benefits of Multiple-Input/Multiple-Output (MIMO) wireless solutions into the airborne environment for maximal effect, the airborne channel must be fully understood. While there have been theoretical models proposed for the airborne channel, there has been very little work toward providing a practical channel model which has been validated by actual an airborne platform. This work presents a characterization of practical performance gains of a MIMO system over a conventional SISO, in a mobile air-to-ground environment. Field measurements were collected with an airborne 4x4 MIMO-OFDM channel-sounding platform at altitudes, speeds and flight patterns approximating medium-endurance vehicles flying over various terrain. Ground stations placed in multiple locations (different scattering scenarios) measured channel responses in addition to actual throughput statistics. Our studies indicate that significant throughput and range gains are achievable with MIMO. We also show that depending on application requirements, these MIMO-enabled gains can be converted into considerable power savings. We also present a study of the effects of introducing MIMO-enabled signaling techniques (such as eigen beamforming and spatial multiplexing) on the total link-capacity of a system of uncoordinated, air-to-ground link-pairs deployed to a single area of operations. Captured channel measurements from the earlier real-world airborne study were inserted into our multi-link simulation environment. Trials were run under several representative aerial-deployment scenarios, revealing significant gains in link capacity. Finally, we consider the potential throughput enhancement delivered by full-duplex signaling and its limitations due to desensitization of receiver hardware by self-generated interference (SI). Existing SI cancellation solutions are prohibitive for long-range/airborne applications due to power handling limitations. They are also not easily scalable for an arbitrary number of MIMO antennas in arbitrary positions. A host-agnostic, high-power, adaptive SI canceler design is proposed and a hardware prototype is presented. Performance enhancement with an off-the-shelf host radio was demonstrated in the presence of varying SI signal profiles.

► Testimonies of “wireless catching up with wireline” have begun. However, the nonstationary and hostile nature of the wireless channel impose the greatest threat to reliable…
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▼ Testimonies of “wireless catching up with wireline” have begun. However, the nonstationary and hostile nature of the wireless channel impose the greatest threat to reliable data transmission over wireless links. The performance of a digital modulation scheme is degraded by many transmission impairments including fading, delay spread, co-channel interference and noise. Two powerful techniques for improving the quality of service over the wireless network are investigated: diversity reception and adaptive error control schemes. Owing to the growing interest in wirelesscommunications, the importance of exact theoretical analysis of such systems cannot be understated. In light of these considerations, this dissertation focuses on accurate and efficient analysis of wireless digital communication systems in multiuser and multipath fading environments.
The evaluation of error probabilities in digital communication systems is often amenable to calculating a generic error probability of the form Pr {X ≤ 0}, where X is a random variable whose probability distribution is known. We advocate a simple numerical approach based on the Fourier or Laplace inversion formulas and Gauss-Chebychev quadratures (GCQ) for computing this error probability. Using this result, and by formulating the outage probability of cellular mobile radio networks in the framework of statistical decision theory, we can unify the outage performance analysis for cellular mobile radio systems in generalized fading channels without imposing any restrictions on the desired signal and interferers statistics.
Next, we develop two unified analytical frameworks for evaluating the bit or symbol error probability (SER) of a broad class of coherent, differentially coherent and noncoherent digital communication systems with diversity reception in generalized fading channels. The exact SER is mostly expressed in terms of a single finite-range integral, and in some cases in the form of double finite-range integrals. Virtually “exact” closed-form expressions (in terms of a rapidly converging series) are also derived. This offers a convenient method to perform a comprehensive study of all common diversity combining techniques (maximal-ratio combining (MRC), equal-gain combining (EGC), selection combining (SDC) and switched combining (SWC)) with different modulation formats in a myriad of fading scenarios. In particular, our unified approach based on characteristic function (CHF) method allows us to unify the above problem in a single common framework. Nevertheless, the moment generating function (MGF) method often yields a more concise solution than the CHF approach in the analysis of MRC, SDC and SWC diversity systems.
Subsequently, we examine the performance of a maximum amplitude selection diversity (MA/SD) rake receiver configuration in indoor wireless channels. The proposed low-complexity receiver structure is practically appealing because of its simplicity as well as its ability to operate effectively even at high signalling rates. We have also devised a…
Advisors/Committee Members: Bhargava, Vijay K. (supervisor).

► In modern communication systems, the rate of transmitted data is growing rapidly. This leads to the need for more sophisticated methods and techniques of implementation…
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▼ In modern communication systems, the rate of transmitted data is growing rapidly. This leads to the need for more sophisticated methods and techniques of implementation in every block of the transmitter-receiver chain. The weakest link in radio communications is the transmission channel. The signal, which is passed through it, suffers from many degrading factors like noise, attenuation, diffraction, scattering etc. In the receiver side, the modulated signal has to be restored to its initial state in order to extract the useful information. Assuming that the channel acts like a filter with finite impulse, one has to know its coefficients in order to apply the inverse function, which will restore the signal back to its initial state. The techniques which deal with this problem are called channel estimation. Noise is one of the causes that degrade the quality of the received signal. If it could be discarded, then the process of channel estimation would be easier. Transmitting special symbols, called pilots with known amplitude, phase and position to the receiver and assuming that the noise has zero mean, an averaging process could reduce the noise impact to the pilot amplitudes and thus simplify the channel estimation process. In this thesis, a novel channel estimation method based on noise rejection is introduced. The estimator takes into account the time variations of the channel and adapts its buffer size in order to achieve the best performance. Many configurations of the estimator were tested and at the beginning of the research fixed size estimators were tested. The fixed estimator has a very good performance for channels which could be considered as stationary in the time domain, like Additive White Gaussian Noise (AWGN) channels or slowly time-varying channels. AWGN channel is a channel model where the only distorting factor is the noise, where noise is every unwanted signal interfering with the useful signal. The properties of the noise are that it is additive, which means that the noise is superimposed on the transmitted signal, it is white so the power density is constant for all frequencies, and it has a Gaussian distribution in the time domain with zero mean and variance σ2=N. A slowly time varying channel refers to channel with coherence time larger than the transmitted symbol duration. The performance of a fixed size averaging estimator in case of fast time-varying channels is subject to the buffering time. When the buffering time is smaller or equal to a portion of the coherence time the averaging process offers better performance than the conventional estimation, but when the buffering time exceeds this portion of the coherence time the performance of the averaging process degrades fast. So, an extension has been made to the averaging estimator that estimates the Doppler shift and thus the coherence time, where the channel could be assumed as stationary. The improved estimator called Adaptive Averaging Channel Estimator (AACE) is capable to adjust its buffer size and thus to average only successive…

► Opportunistic beamforming is a reduced feedback communication strategy for vector broadcast channels which only requires partial channel state information (CSI) at the base station for…
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▼ Opportunistic beamforming is a reduced feedback communication strategy for vector broadcast channels which only requires partial channel state information (CSI) at the base station for its operation. Although reducing feedback, this strategy, in its plain implementations, displays a linear growth in the feedback load with the total number of users in the system, which can be an onerous requirement for large systems. This impracticality motivates the use of selective feedback techniques in which only the users with good channels are allowed to feedback. In this thesis, we focus on a more stringent but practical finite limit on the feedback load, and we study the structure of the sum-rate maximizing decentralized selective feedback policies, and how the resulting sum-rate compare to the sum-rate without any user selection.
Firstly, we set up the problem of finding the structure of downlink sum-rate maximizing selective decentralized feedback policies for opportunistic beamforming under finite feedback constraints on the average number of mobile users feeding back. We show that any sum-rate maximizing selective decentralized feedback policy must be a threshold feedback policy. This result holds for most practical fading channel models.
Then, the resulting optimum threshold selection problem is analyzed in detail. This is a non-convex optimization problem over finite dimensional Euclidean spaces. By utilizing the theory of majorization, an underlying Schur-concave structure in the sum-rate function is identified, and the sufficient conditions for the optimality of homogenous threshold feedback policies are obtained. Applications of these results are illustrated for well known fading channel models such as Rayleigh, Nakagami and Rician fading channels, along with various engineering and design insights. Rather surprisingly, it is shown that using the same threshold value at all mobile users is not always a rate-wise optimal feedback strategy, even for a network with statistically identical mobile users. For the Rayleigh fading channel model, on the other hand, homogenous threshold feedback policies are proven to be rate-wise optimal if multiple orthonormal data carrying beams are used to communicate with multiple mobile users simultaneously.
Having established the optimality of a homogenous threshold for a multi-beam Rayleigh fading environment, we then analyze the derivation of these optimum policies which ensure a O (1) feedback constraint as the number of users grows large. Starting with a set of statistically identical users, we obtain the tradeoff curve tracing the Pareto optimal boundary between feasible and infeasible feedback-capacity pairs for opportunistic beamforming. Any point on this tradeoff curve can be obtained by means of the derived threshold feedback policies, which are rate-wise optimal. We further show to what extent the O (1) feedback constraint must be relaxed to…

► Next Generation Wireless Networks (NGWNs) are envisaged to be heterogeneous. They will integrate multiple Radio Access Technologies (RATs) on the same platform where the RAT…
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▼ Next Generation Wireless Networks (NGWNs) are envisaged to be heterogeneous. They will integrate multiple Radio Access Technologies (RATs) on the same platform where the RAT s are expected to work together in a coordinated fashion. Radio resources will therefore be jointly managed. Joint Call Admission Control (JCAC) approach has been adopted to jointly allocate or handle the radio resources amongst the different RATs in an NGWN. A number of JCAC algorithms have been proposed in the literature with the objective of enabling efficient utilisation of the radio resources and ensuring that required QoS requirements are met . However, studies in JCAC have not typically considered the revenue obtained by network operators in NGWNs . With the implementation of NGWNs, user demand for network services is expected to significantly increase. Consequently, one of the challenges envisaged in the NGWNs for network operators is a large decoupling between users' traffic and the revenue obtained . Therefore, it is important to analyse the network operators' revenue in NGWN s and devise means to ensure that sufficient revenue is obtained. This research analyses network operators' revenue in a heterogeneous network environment while maintaining QoS by incorporating pricing in JCAC. An analytical model based on a multi-dimensional Markov decision process is used to model JCAC algorithm in an NGWN. The JCAC algorithm used is load-based whereby calls arriving in the network are admitted to the least loaded RATs. The performance of the algorithm is evaluated using MATLAB. The analysed NGWN consists of two RATs and two service classes. QoS performance is measured with connection-level QoS metrics namely call blocking probability and call dropping probability. Other investigated performance metrics are average number of calls in the systems, user utility and revenue obtained. Performance of the NGWN is carried out with a dynamic pricing scheme incorporated in JCAC. A discount approach is applied to determine new price under the dynamic pricing scheme. User behaviour with price variation is impacted by change of call arrival rate and average call duration. Simulations are also carried out with flat pricing for comparison purposes. The results obtained show that better system performance and high revenue for network operators are obtained with the dynamic pricing scheme. Furthermore, a hybrid pricing model is proposed whereby flat and dynamic pricing schemes are integrated, giving users flexibility of choosing an appropriate pricing scheme. The analysis is conducted with different percentages of users opting for either dynamic or flat pricing schemes. Simulation results show that higher user utility and improved QoS performance are obtained with the hybrid pricing model. Additionally, reasonable operators' revenue is guaranteed with the hybrid pricing model.
Advisors/Committee Members: Falowo, Olabisi E (advisor).

Kabahuma, S. (2010). Joint call admission control incorporating pricing for congestion control to enhance QoS and ensure revenue for network operators in next generation wireless networks. (Thesis). University of Cape Town. Retrieved from http://hdl.handle.net/11427/14594

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Kabahuma, Sarah. “Joint call admission control incorporating pricing for congestion control to enhance QoS and ensure revenue for network operators in next generation wireless networks.” 2010. Thesis, University of Cape Town. Accessed September 15, 2019.
http://hdl.handle.net/11427/14594.

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Kabahuma S. Joint call admission control incorporating pricing for congestion control to enhance QoS and ensure revenue for network operators in next generation wireless networks. [Thesis]. University of Cape Town; 2010. Available from: http://hdl.handle.net/11427/14594

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

Cooperative diversity has been proposed as a powerful means to enhance the performance of high-rate communications over wireless fading channels. It realizes spatial diversity advantages in a distributed manner where two or more nodes share their antennas to mimic a virtual antenna array.

► Advances in wireless technology and an increasing demand for new applications that require in-field communication are generating more interest in off-road vehicular networks than ever…
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▼ Advances in wireless technology and an increasing demand for new applications that require in-field communication are generating more interest in off-road vehicular networks than ever before. Current on-road and off-road vehicular networking technologies are either cost prohibitive, bandwidth limited, or exhibit too much latency. 802.11 standard networks are a low-cost, readily available technology that have the potential of integrating effectively with current off road equipment software and hardware.
The main objective of this research was to develop a baseline for the performance of an 802.11b/g wireless network in a realistic in-field agricultural environment. While recognizing there are many external factors that can degrade the performance and reliability of such a system, this research was focused on identifying and measuring the performance effects of varying parameters that can be controlled, in particular the data rate, packet size, and the choice of 802.11b versus 802.11g protocols.
The performance of the system was measured by recording packets at both the transmitting and receiving devices and calculating the percentage of packets received at varying distances between the nodes. A simple two node network between two tractors was constructed for performance testing, and an application was written that used personal computers on each tractor to generate and log network traffic simultaneously. A series of 18 tests were executed with varying data rates, protocols, and packet sizes in realistic in-field conditions. Data were then post-processed so that they could be easily analyzed with the aid of Microsoft ExcelTM.
The 802.11b network performed much better in the outdoor environment by transmitting data more reliably and farther than the 802.11g network. 802.11g networks exhibited a high reliability region, usually at small distances between nodes, and a region with less reliability, at larger distances between nodes. Increasing 802.11g data rates decreased the distance over which the network would reliably transmit, but increasing 802.11b data rates had little effect on maximum transmission distance, although they decreased the overall reliability of the network. For packets between 15 and 1400 bytes in length, small but statistically significant decreases in reliability were observed with increasing packet size. For the largest packet size of 2200 bytes, more notable reliability decreases were observed. The network performance was influenced by the angle of the transmitted wave relative to the tractor orientation. Finally, performance degradation due to signal reflections off the soil surface could be observed at distinct distances between nodes.
Advisors/Committee Members: Hansen, Alan C. (advisor).

▼ Multiple-input, multiple-output (MIMO) wireless communication systems combine the deployment of multiple antennas at both the transmitter and receiver with sophisticated signal processing to improve the performance of wirelesscommunications. As with any communication system, developing an accurate yet mathematically tractable channel model is essential to analyzing the performance of actual systems. Prior studies of MIMO channel modeling have provided detailed models for fading correlation – either due to the
propagation environment or through mutual coupling between the antennas – and how this correlation affects performance. On the other hand, relatively little attention has been paid to the noise correlation.
In this dissertation we consider noise analysis and low-noise design for compact MIMO receivers. We begin by analyzing the performance of several MIMO communication schemes in the presence of fading and noise correlation. It is shown that fading and noise correlation have opposite effects on performance, so properly accounting for
both in the channel model is crucial to accurately predicting performance. Next we develop a circuit model for compact multi-antenna receivers that includes noise generated by the antennas, front-end amplifiers, and other components. Through analytical and numerical examples we demonstrate that the noise may
be correlated, and that different noise sources may impact performance in profoundly different ways. Finally, we derive low-noise design theorems for MIMO front-ends from communication-theoretic principles.
Advisors/Committee Members: Brian L. Hughes, Committee Chair (advisor), Kevin G. Gard, Committee Member (advisor), Gianluca Lazzi, Committee Member (advisor), J. Keith Townsend, Committee Member (advisor), Stephen L. Campbell, Committee Member (advisor).

► Pointing, acquisition and tracking of a free-space optical node in a mobile network experiencing misalignment due to adverse factors including vibration, motion and atmospheric turbulence…
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▼ Pointing, acquisition and tracking of a free-space optical node in a mobile network experiencing misalignment due to adverse factors including vibration, motion and atmospheric turbulence requires a different approach than traditional free-space optical transceivers. A recent fiber-bundle approach for beam steering at the transmitter was investigated to provide continuous beam coverage at the receiver without the application of mechanical devices. Utilizing multiple fibers-lenses sets at the receiver was also proposed to enhance the tolerance of optical link misalignment. In this work, both laboratory experiments and software simulation were implemented to evaluate the optical link performance for different fiber-bundle-based transceiver setups as the link parameters were varied. The performance was evaluated in terms of the coverage area at the receiver, which is a measure of misalignment tolerance and is dependent not only on wavelength but on other key parameters such as link length, transmitted power, the pattern of transmitters, beam divergence, and the receiver construction. The results showed that fiber-bindle-based transceivers reveal significant potential to maximize the up time of the link, and the results also provide guidance on the further development of the overall system. To incorporate the proposed transceiver designs, an alignment control system was developed and evaluated as well. The laboratory results show that the optical control system successfully recovered and maintained the link while the receiver was in motion and the signal coverage at the target area was enhanced significantly.
Advisors/Committee Members: Refai, Hazem H.||LoPresti, Peter G. (advisor).

▼ Cooperative Spectrum Sensing (CSS) allows Cognitive Radio Networks (CRNs) to locate vacant spectrum channels and to protect active Primary Users (PUs). However, the achieved detection accuracy is proportional to the duration of the CSS process which, unfortunately, reduces the time of useful communication as well as increases the Co-Channel Interference (CCI) perceived by an active PU. To overcome this, this thesis proposes three CSS strategies, namely the Dual-Threshold CSS (DTCSS), the Maximum CSS (MCSS), and the Max-Min CSS (MMCSS). These strategies reduce the number of reporting terminals while maintaining reliable performance and minimal CCI effect. The performance of these three methods is analyzed, and the numerical and simulations results illustrate the accuracy of the derived results as well as the achieved performance gains. The second part of this thesis studies the impact of CCI on the performance of a number of transmission techniques used by CRNs. These are Chase combining Hybrid Automatic Repeat Request (HAQR), Fixed Relaying (FR), Selective Relaying (SR), Incremental Relaying (IR), and Selective Incremental Relaying (SIR). The performance of these techniques is studied in terms of the average spectral efficiency, the outage probability, and the error probability. To obtain closed forms for the error probabilities, this thesis proposes a novel accurate approximation of the exponential integral function using a sum of exponentials.

► This thesis focuses on the design of algorithms for resource allocation and feedback in wireless multiuser and heterogeneous networks. In particular, three key design challenges…
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▼ This thesis focuses on the design of algorithms for resource allocation and feedback in wireless multiuser and heterogeneous networks. In particular, three key design challenges expected to have a major impact on future wireless networks are considered: cross-layer scheduling; structured quantization codebook design for MU-MIMO networks with limited feedback; and resource allocation to provide physical layer security.
The first design challenge is cross-layer scheduling, where policies are proposed for two network architectures: user scheduling in single-cell multiuser networks aided by a relay; and base station (BS) scheduling in CoMP. These scheduling policies are then analyzed to guarantee satisfaction of three performance metrics: SEP; packet delay; and packet loss probability (PLP) due to buffer overflow. The concept of the τ-achievable PLP region is also introduced to explicitly describe the tradeoff in PLP between different users.
The second design challenge is structured quantization codebook design in wireless networks with limited feedback, for both MU-MIMO and CoMP. In the MU-MIMO network, two codebook constructions are proposed, which are based on structured transformations of a base codebook. In the CoMP network, a low-complexity construction is proposed to solve the problem of variable codebook dimensions due to changes in the number of coordinated BSs. The proposed construction is shown to have comparable performance with the standard approach based on a random search, while only requiring linear instead of exponential complexity.
The final design challenge is resource allocation for physical layer security in MU-MIMO. To guarantee physical layer security, the achievable secrecy sum-rate is explicitly derived for the regularized channel inversion (RCI) precoder. To improve performance, power allocation and precoder design are jointly optimized using a new algorithm based on convex optimization techniques.

►Wireless-powered communication is an emerging technology for powering the large number of miniature devices of the future. In a wireless-powered communication system, low-power sensors extract…
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▼Wireless-powered communication is an emerging technology for powering the
large number of miniature devices of the future. In a wireless-powered communication system, low-power sensors extract energy from the incident wireless signals to
power their operations such as information transmission, sensing or reception. Due to sporadic energy availability, however, such a system is fundamentally different from
a traditionally-powered communication system. This dissertation investigates three distinct aspects of wireless-powered communications to get insights on the system operation. First, leveraging concepts from finite-length information theory, an analytical framework is developed for examining wireless-powered communications with short packets, i.e., in the finite blocklength regime. This is relevant as remotely-powered communications may entail short packets due to small payloads, low-latency requirements, or limited energy to support a longer transmission. Second, using a stochastic geometry framework, an analytical model is developed for characterizing the performance of wireless-powered communications in the millimeter wave (mmWave) band. The proposed model incorporates the key features of mmWave systems such as directional beamforming and sensitivity to building blockages. Finally, the power transfer efficiency and the energy efficiency of a wireless-powered communication system aided by massive MIMO is characterized. The broad goal of this dissertation is to better understand wireless-powered communications in the context of the emerging technologies for 5G.
Advisors/Committee Members: Heath, Robert W., Jr, 1973- (advisor), Andrews, Jeffrey G (committee member), Thomaz Jr., Edison (committee member), Vikalo, Haris (committee member), Orlik, Philip (committee member).

▼ The growing PHY layer capabilities of WiFi has made it possible to reuse WiFi signals for sensing. Sensing via WiFi enables remote sensing without wearable sensors and contactless sensing in privacy-preserving mode, which are beneficial in various applications including security surveillance, intrusion detection, elderly monitoring, and human-computer interaction. For WiFi sensing to excel indoors, multipath propagation acts as a major concern. The multipath effect can invalidate theoretical propagation models, distort received signal signatures, and constrain the performance of wireless sensing even when inferring the presence of humans. To explicitly eliminate any adverse impact of multipath propagation, researchers resort to customized signals and specialized software-defined radios for radar signal processing. To enable device-free applications on commodity infrastructures, existing approaches exploit a dense deployment of wireless links. Instead of avoiding multipath, in this thesis, we demonstrate it is possible to harness multipath in WiFi sensing with the PHY layer Channel State Information (CSI). First, we design a primitive to identify the availability of the LOS path under multipath propagation with only commodity WiFi devices to improve the multipath awareness in WiFi sensing. Second, we exploit the rich multipath effect as fingerprints to blur the directional coverage of traditional passive human detection architecture to achieve omnidirectional coverage. Third, we propose a measurable metric as proxy for detection sensitivity and a lightweight subcarrier and path configuration scheme to adapt to different multipath propagation conditions. Finally, we design a unified framework for both static and moving human detection, by capturing the chest movements of static humans. We prototype the above schemes with commodity WiFi infrastructure, and evaluate their performances in typical office environments. Experimental results demonstrate improved detection accuracy, coverage and sensitivity compared with MAC layer RSSI based schemes.

► In multiuser wirelesscommunications, interference not only limits the performance of the system, but also allows users to eavesdrop on other users’ messages. Hence, interference…
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▼ In multiuser wirelesscommunications, interference not only limits the performance of the system, but also allows users to eavesdrop on other users’ messages. Hence, interference management in multiuser wireless communication has received significant attention in the last decade, both in the academia and industry. The interference channel (IC) is one of the simplest information theoretic models to analyze the effect of interference on the throughput and secrecy of individual messages in a multiuser setup. In this thesis, the IC is studied under different settings with and without the secrecy constraint. The main contributions of the thesis are as follows:
• The generalized degrees of freedom (GDOF) has emerged as a useful approximate measure of the potential throughput of a multiuser wireless system. Also, multiple antennas at the transmitter and receiver can provide additional dimension for signaling, which can in turn improve the GDOF performance of the IC. In the initial part of the thesis, a K-user MIMO Gaussian IC (GIC) is studied from an achievable GDOF perspective. An inner bound on GDOF is derived using a combination of techniques such as treating interference as noise, zero-forcing receiving, interference alignment (IA), and extending the Han-Kobayashi (HK) scheme to K users. Also, outer bounds on the sum rate of the K-user MIMO GIC are derived, under different assumptions of cooperation and providing side information to the receivers. The derived outer bounds are simplified to obtain outer bounds on the GDOF. The relative performance of these bounds yields insight into the performance limits of the multiuser MIMO GIC and the relative merits of different schemes for interference management.
• Then, the problem of designing the precoding and receive filtering matrices for IA is explored for K-user MIMO (M × N) GIC. Two algorithms for designing the precoding and receive filtering matrices for IA in the block fading or constant MIMO IC with a finite number of symbol extensions are proposed. The first algorithm for IA is based on aligning a subset of the interfering signal streams at each receiver. As the first algorithm requires global channel knowledge at each node, a distributed algorithm is proposed which requires only limited channel knowledge at each node. A new performance metric is proposed, that captures the possible loss in signal dimension while designing the precoders. The performance of the algorithms are evaluated by comparing them with existing algorithms for IA precoder design.
• In the later part of the thesis, a 2-user IC with limited-rate transmitter cooperation is studied, to investigate the role of cooperation in managing interference and ensuring secrecy. First, the problem is studied in the deterministic setting, and achievable schemes are proposed, which use a combination of interference cancelation, relaying of the other user’s data bits, time sharing, and transmission of random bits, depending on the rate of the cooperative link and the relative strengths of the signal and the…
Advisors/Committee Members: Murthy, Chandra R.

► In multiuser wirelesscommunications, interference not only limits the performance of the system, but also allows users to eavesdrop on other users’ messages. Hence, interference…
(more)

▼ In multiuser wirelesscommunications, interference not only limits the performance of the system, but also allows users to eavesdrop on other users’ messages. Hence, interference management in multiuser wireless communication has received significant attention in the last decade, both in the academia and industry. The interference channel (IC) is one of the simplest information theoretic models to analyze the effect of interference on the throughput and secrecy of individual messages in a multiuser setup. In this thesis, the IC is studied under different settings with and without the secrecy constraint. The main contributions of the thesis are as follows:
• The generalized degrees of freedom (GDOF) has emerged as a useful approximate measure of the potential throughput of a multiuser wireless system. Also, multiple antennas at the transmitter and receiver can provide additional dimension for signaling, which can in turn improve the GDOF performance of the IC. In the initial part of the thesis, a K-user MIMO Gaussian IC (GIC) is studied from an achievable GDOF perspective. An inner bound on GDOF is derived using a combination of techniques such as treating interference as noise, zero-forcing receiving, interference alignment (IA), and extending the Han-Kobayashi (HK) scheme to K users. Also, outer bounds on the sum rate of the K-user MIMO GIC are derived, under different assumptions of cooperation and providing side information to the receivers. The derived outer bounds are simplified to obtain outer bounds on the GDOF. The relative performance of these bounds yields insight into the performance limits of the multiuser MIMO GIC and the relative merits of different schemes for interference management.
• Then, the problem of designing the precoding and receive filtering matrices for IA is explored for K-user MIMO (M × N) GIC. Two algorithms for designing the precoding and receive filtering matrices for IA in the block fading or constant MIMO IC with a finite number of symbol extensions are proposed. The first algorithm for IA is based on aligning a subset of the interfering signal streams at each receiver. As the first algorithm requires global channel knowledge at each node, a distributed algorithm is proposed which requires only limited channel knowledge at each node. A new performance metric is proposed, that captures the possible loss in signal dimension while designing the precoders. The performance of the algorithms are evaluated by comparing them with existing algorithms for IA precoder design.
• In the later part of the thesis, a 2-user IC with limited-rate transmitter cooperation is studied, to investigate the role of cooperation in managing interference and ensuring secrecy. First, the problem is studied in the deterministic setting, and achievable schemes are proposed, which use a combination of interference cancelation, relaying of the other user’s data bits, time sharing, and transmission of random bits, depending on the rate of the cooperative link and the relative strengths of the signal and the…
Advisors/Committee Members: Murthy, Chandra R.

► Filters are one of the essential components in the RF and wireless communication systems. Small sized planar lowpass filters with good electrical characteristics along with…
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▼ Filters are one of the essential components in the RF and wireless
communication systems. Small sized planar lowpass filters with good electrical
characteristics along with low cost, light weight and ease of fabrication are highly
desirable for the front end of modern communication systems to suppress harmonics
and spurious signals. Design of compact lowpass filters with improved performance
and diverse specifications for numerous applications is a huge challenge.
In this thesis, high performance planar compact lowpass filters using multiple
patch resonators on high impedance transmission line are developed. Design techniques
of different types of patch resonators and their modifications to enhance the
performance of the filters are presented.Patch resonators are designed by using high impedance short circuited stubs
and low impedance open circuited patches. In the first stage of filter realization,
compact lowpass filter having sharp roll-off using triangular and funnel patch
resonators is presented. The structure is modified further to enhance the relative
stopband bandwidth of the filter. In the third stage, another resonator has been
introduced near the feed line to achieve sharp roll-off for the same cutoff frequency,
stopband bandwidth and suppression level. To obtain compactness, high suppression
level and wide stopband in filter design, low thickness substrate is tested and proved in
the fourth stage.
Realizations of planar compact lowpass filter with very sharp roll-off near the
cutoff frequency have been presented using stepped impedance polygonal patch
resonators. By increasing the patch size and number of resonators, the stopband
bandwidth and suppression level have to be enhanced to a great extent. Enhancement
of performance characteristics of lowpass filter design is continually being extended.
By using high value capacitance patch, the stopband suppression level of the filter with
sharp roll-off rate is achieved. Elliptic function lowpass filter with ultra-sharp roll-off is
also developed using elliptic shaped patch resonators.
Throughout the study, low cost substrate having permittivity 4.4 is used for the
filter design. All the designed filters have been fabricated and predicted results are
validated by the measurements.

Raphika, P. M. (2016). Design and Development of Planar Lowpass Filters with Sharp Roll-off and Wide Stopband for RF and Wireless Communication Systems. (Thesis). Cochin University of Science and Technology. Retrieved from http://dyuthi.cusat.ac.in/purl/5170

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Raphika, P M. “Design and Development of Planar Lowpass Filters with Sharp Roll-off and Wide Stopband for RF and Wireless Communication Systems.” 2016. Thesis, Cochin University of Science and Technology. Accessed September 15, 2019.
http://dyuthi.cusat.ac.in/purl/5170.

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Raphika PM. Design and Development of Planar Lowpass Filters with Sharp Roll-off and Wide Stopband for RF and Wireless Communication Systems. [Thesis]. Cochin University of Science and Technology; 2016. Available from: http://dyuthi.cusat.ac.in/purl/5170

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

► Multivariate statistics play an important role in performance analysis of wireless communication systems in correlated fading channels. This thesis presents a framework which can be…
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▼ Multivariate statistics play an important role in
performance analysis of wireless communication systems in
correlated fading channels. This thesis presents a framework which
can be used to derive easily computable mathematical
representations for some multivariate statistical distributions,
which are derivatives of the Gaussian distribution, and which have
a particular correlation structure. The new multivariate
distribution representations are given as single integral solutions
of familiar mathematical functions which can be evaluated using
common mathematical software packages. The new approach can be used
to obtain single integral representations for the multivariate
probability density function, cumulative distribution function, and
joint moments of some widely used statistical distributions in
wireless communication theory, under an assumed correlation
structure. The remarkable advantage of the new representation is
that the computational burden remains at numerical evaluation of a
single integral, for a distribution with an arbitrary number of
dimensions. The new representations are used to evaluate the
performance of diversity combining schemes and multiple input
multiple output systems, operating in correlated fading channels.
The new framework gives some insights into some long existing open
problems in multivariate statistical distributions.

► The broad theme of this work is in constructing optimal transmission mechanisms for a wide variety of communication systems. In particular, this dissertation provides a…
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▼ The broad theme of this work is in constructing optimal transmission mechanisms for a wide variety of communication systems. In particular, this dissertation provides a proof of threshold saturation for spatially-coupled codes, low-complexity capacity-achieving coding schemes for side-information problems, a proof that Reed-Muller and primitive narrow-sense BCH codes achieve capacity on erasure channels, and a mathematical framework to design delay sensitive communication systems.
Spatially-coupled codes are a class of codes on graphs that are shown to achieve capacity universally over binary symmetric memoryless channels (BMS) under belief-propagation decoder. The underlying phenomenon behind spatial coupling, known as ?threshold saturation via spatial coupling?, turns out to be general and this technique has been applied to a wide variety of systems. In this work, a proof of the threshold saturation phenomenon is provided for irregular low-density parity-check (LDPC) and low-density generator-matrix (LDGM) ensembles on BMS channels. This proof is far simpler than published alternative proofs and it remains as the only technique to handle irregular and LDGM codes. Also, low-complexity capacity-achieving codes are constructed for three coding problems via spatial coupling: 1) rate distortion with side-information, 2) channel coding with side-information, and 3) write-once memory system. All these schemes are based on spatially coupling compound LDGM/LDPC ensembles.
Reed-Muller and Bose-Chaudhuri-Hocquengham (BCH) are well-known algebraic codes introduced more than 50 years ago. While these codes are studied extensively in the literature it wasn?t known whether these codes achieve capacity. This work introduces a technique to show that Reed-Muller and primitive narrow-sense BCH codes achieve capacity on erasure channels under maximum a posteriori (MAP) decoding. Instead of relying on the weight enumerators or other precise details of these codes, this technique requires that these codes have highly symmetric permutation groups. In fact, any sequence of linear codes with increasing blocklengths whose rates converge to a number between 0 and 1, and whose permutation groups are doubly transitive achieve capacity on erasure channels under bit-MAP decoding. This pro-vides a rare example in information theory where symmetry alone is su?cient to achieve capacity.
While the channel capacity provides a useful benchmark for practical design, communication systems of the day also demand small latency and other link layer metrics. Such delay sensitive communication systems are studied in this work, where a mathematical framework is developed to provide insights into the optimal design of these systems.
Advisors/Committee Members: Chamberland, Jean-Francois (advisor), Pfister, Henry D (advisor), Shakkottai, Srinivas (committee member), Papanikolas, Matthew A (committee member).

► Quality-of-service (QoS) guarantees will play a critically important role in future mobile wireless networks. In this dissertation, we study a set of QoS-driven resource allocation…
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▼ Quality-of-service (QoS) guarantees will play a critically important role in future
mobile wireless networks. In this dissertation, we study a set of QoS-driven resource
allocation problems for mobile wirelesscommunications and networks.
In the first part of this dissertation, we investigate resource allocation schemes
for statistical QoS provisioning. The schemes aim at maximizing the system/network
throughput subject to a given queuing delay constraint. To achieve this goal, we
integrate the information theory with the concept of effective capacity and develop
a unified framework for resource allocation. Applying the above framework, we con-sider a number of system infrastructures, including single channel, parallel channel,
cellular, and cooperative relay systems and networks, respectively. In addition, we
also investigate the impact of imperfect channel-state information (CSI) on QoS pro-visioning. The resource allocation problems can be solved e?ciently by the convex
optimization approach, where closed-form allocation policies are obtained for different
application scenarios.
Our analyses reveal an important fact that there exists a fundamental tradeoff
between throughput and QoS provisioning. In particular, when the delay constraint
becomes loose, the optimal resource allocation policy converges to the water-filling
scheme, where ergodic capacity can be achieved. On the other hand, when the
QoS constraint gets stringent, the optimal policy converges to the channel inversion scheme under which the system operates at a constant rate and the zero-outage
capacity can be achieved.
In the second part of this dissertation, we study adaptive antenna selection for
multiple-input-multiple-output (MIMO) communication systems. System resources
such as subcarriers, antennas and power are allocated dynamically to minimize the
symbol-error rate (SER), which is the key QoS metric at the physical layer. We
propose a selection diversity scheme for MIMO multicarrier direct-sequence code-
division-multiple-access (MC DS-CDMA) systems and analyze the error performance
of the system when considering CSI feedback delay and feedback errors. Moreover,
we propose a joint antenna selection and power allocation scheme for space-time
block code (STBC) systems. The error performance is derived when taking the CSI
feedback delay into account. Our numerical results show that when feedback delay
comes into play, a tradeoff between performance and robustness can be achieved by
dynamically allocating power across transmit antennas.
Advisors/Committee Members: Zhang, Xi (advisor), Chen, Jianer (committee member), Georghiades, Costas N. (committee member), Reddy, A. L. Narasimha (committee member).

► The objectives of the project are to simulate and test a broadband microstrip balun to operate at a center frequency of 5 GHz and 50%…
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▼ The objectives of the project are to simulate and test a broadband microstrip balun to operate at a center frequency of 5 GHz and 50% bandwidth. The balun design finds extensive applications in the modern wirelesscommunications particularly in accomplishing frequency conversion mixers to make cellular phone and data transmission networks possible. They are used to link symmetrical (balanced) circuit to asymmetrical (unbalanced) circuit in design of mixers and push pull amplifiers. The simulation of the circuit is done in Advanced Design System (ADS) software. The balun is designed to convert signals from a single-ended, unbalanced mode to a balanced mode, having two signals of equal balance impedance but shifted 180-degree in phase over the specified frequency range with minimum loss and low voltage standing wave ratio (VSWR). The goals of the design are to achieve high phase, amplitude balance and low VSWR with good performance results.
Advisors/Committee Members: Kumar, Preetham.